Resistivity minima and Kondo effect in ferromagnetic GaMnAs films

The temperature dependence of the resistivity of ferromagnetic GaMnAs, as-grown or low-temperature-annealed samples is measured from 2to290K. A resistivity minimum is observed with a corresponding temperature TM around 10K for each sample. Below TM, the resistivity exhibits logarithmic temperature dependence, as αln(T), and α is independent of the external magnetic field up to 9T. Such behavior is explained in terms of the Kondo effect arising from the presence of Mn interstitials in the GaMnAs samples. In addition, a well-defined T-squared dependence of resistivity is found in the temperature range between TM and the Curie temperature (TC), which is attributed to single magnon scattering.